There are several reports showing different MMP expression patterns in melanoma [6
] but, to the best of our knowledge, this is the first genetic study to examine the role of polymorphisms in MMP-9
in melanoma progression and other melanoma risk factors. We hypothesized that the MMP-9
polymorphisms might alter the expression and activity of the enzyme, increasing ECM degradation and invasion, leading to melanoma progression.
Gene transcription is the primary point of regulation of MMPs; therefore, sequence changes in the promoter may have important implications for the transcription, and in turn, for the protein levels and cell physiology. This led us to assess previously described functional polymorphisms within the promoter region of MMP-9: (-)1562 C > T and (-)131 (CA)n.
The polymorphism at position (-)1562 changes the promoter activity of MMP-9
because the T allele abolishes a binding site for a transcription repressor [36
]. Although the less active C allele was expected to be present in less aggressive lesions, we found the opposite results. A similar association between this SNP and breast cancer was found by Grieu et al
, where the T allele correlated with non-ductal histology, positive estrogen receptor and absence of TP53 mutations in breast cancer [37
]. However, Matsumura et al
found significant associations between this allele and the invasive phenotype of gastric cancer [38
]. These divergent results indicate that there might be other factors that play a role in the regulation of the MMP-9
transcription and/or activity, such as other regulatory elements, promoter methylation or even other steps such as secretion and type of cells under study [39
The dinucleotide repeat shows a bimodal distribution (reviewed by Van den Steen et al
]), with the most prevalent allele being (CA)14
and a second peak at (CA)21–23
in American white, Finnish, Swedish, Belgian, African-American and southern English population. On the other hand, the Japanese population show the highest incidence of (CA)21
followed by (CA)> 21
. Similar to the SNP at position (-)1562, the length of the microsatellite may influence the transcriptional activity of the gene due to its close localization to the transcriptional start site and several transcription factor binding sites and its length-dependent interaction with nuclear proteins [31
]. However, data are inconsistent with regard to the relationship between the length of the microsatellite and the promoter activity [30
]. Our analysis showed the same distribution and that short alleles were present more frequently in patients at higher risk for melanoma.
There are no published data on the effect of the coding polymorphisms in the MMP-9 activity therefore; it is not possible to hypothesize which variants could be associated with advanced stages of the disease and/or shorter progression-free survival. In this analysis, we found that the reference alleles were more frequent among patients with higher risk for melanoma development (tendency to sunburn, family history of melanoma), more advanced disease (higher melanoma stage, presence of intransit metastasis), and desmoplastic melanoma. However, after adjustment for age, sex, phenotypic index, moles, and freckles only four of these associations remained significant. The 279QQ genotype was associated with the presence of intransit metastasis (padjusted
= 0.02) and tendency to sunburn (padjusted
< 0.01); the 574R allele was more common among patients with melanomas in the extremities (padjusted
= 0.02); and 668RR was associated with the tendency to sunburn (padjusted
= 0.02). Our genotyping results suggest that the "reference" MMP-9 enzyme is more active than the "variant" product. These observations agree with the results of a very recent case-control study conducted in Japanese that suggests a link between the R279Q polymorphism and malignant potential of renal cell carcinoma [41
Our study subjects included ten patients who were younger than 18 years old at diagnosis. In this particular group, the etiology of the disease may differ from the etiology of melanoma in adults. However, other than the presence of spitzoid melanomas in 4 of 10 of these patients, we did not find any additional withstanding clinicopathological or genotypic characteristic and therefore, they were not excluded from the analysis.
Interestingly, variant alleles (-)1562T and 668Q were more frequent among patients with primary melanomas localized to non-cutaneous sites, mainly mucosal melanomas (90%). Whether there is a significant association between these SNPs and mucosal melanoma remains to be determined in a larger group of patients with this type of the disease.